Method and apparatus for transmitting/receiving signals in multiple-input multiple output communication system provided with plurality of antenna elements

ABSTRACT

A method and apparatus for transmitting/receiving signals in a multiple-input multiple-output communication system provided with a plurality of antenna elements is disclosed. Accordingly, the present invention provides a plurality of antenna groups at one distance having the antenna elements arranged at the other distance, a method and a means for identifying the groups and adding an identifier for the groups. It further provides a method and an apparatus for allocating power for the groups.

This application claims the benefit of U.S. patent application Ser. No.10/274,001 lied Oct. 21, 2002 now U.S. Pat. No. 7,327,798, which claimsthe benefit of the Korean Application Nos. P01-64722 filed on Oct. 19,2001, P02-00417 filed on Jan. 4, 2002, P02-64059 filed on Oct. 19, 2002,and P02-64060 filed on Oct. 19, 2002, the subject matters of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a mobile communicationsystem, and more particularly to a method and an apparatus fortransmitting/receiving signals in a multiple-input multiple-output(MIMO) communication system provided with a plurality of antennaelements.

2. Background of the Related Art

Generally, the multiple-input multiple-output (MIMO) system has beenevolved from a conventional single-input single-output (SISO)communication system and a single-input multiple-output (SIMO)communication system, and developed so that it is used in a techniquethat requires a high-capacity data transmission. This MIMO systemtransmits information through M antennas and receives the informationthrough N antennas, and is considered as an essential element in thefourth-generation communication system that requires a high efficiencyof frequency.

FIG. 1 is a diagram illustrating an example of a conventional MIMOsystem.

Referring to FIG. 1, a transmitter includes a transmissionmultiple-input multiple-output processor 101 for dividing an informationsource (or bit stream or data stream) into M sub-bit streams for signalprocessing, and a modulator 102 for modulating processed signals andapplying modulated signals to M antennas. A receiver includes ademodulator 103 for receiving the signals transmitted from thetransmitter through N antennas and demodulating the received signals,and a reception multiple-input multiple-output processor 104 forprocessing and restoring demodulated signals to the original bit stream.

FIG. 2 is a diagram illustrating an example of a transmitter of aconventional D-BLAST MIMO system. FIG. 3 is a diagram illustrating anexample of a receiver of a conventional D-BLAST MIMO system.

According to the MIMO system of FIGS. 2 and 3, the distance betweenantennas is 1.5λ, and four transmission and reception antennas are used.The MIMO system of FIGS. 2 and 3 is of a diagonal-bell labs' layeredspace-time (D-BLAST) type.

Referring to FIGS. 2 and 3, the bit stream to be transmitted is dividedinto M sub-bit streams of the same ratio by a demultiplexer 203, and thesub-bit streams are encoded in a signal processor 202. The encodedsignals are periodically connected to the respective antennas by atetrad cyclic shifter 201 to be transmitted to the receiver.

The signal processor 202 generates transmission signals having differenttransmission delays by modulating and encoding the respective bitstreams of one information source, and applies the signals to therespective antennas. The signals transmitted through the antennasinclude the symbols encoded from the same information.

The cyclic shifter 201 periodically changes the connection of thetransmission antennas to the signals processed from the sub-streams. Foreach τ seconds, the connection between the processed signals and thetransmission antennas is periodically changed. This enables thetransmitter to use a delay diversity technique, and M processed signalson fading channels are all received through the N receiving antennas.Herein, since the M transmitted signals are received through all thereceiving antennas, any one of the transmitted signals is receivedwithout being seriously affected by the worst channel environment whenit passes through the multiple-paths environment.

Accordingly, the symbols which the received signals include arediagonally detected in respective space layers (discriminated by thereceiving antennas) of a detector 301. That is, the desired symbolvalues are detected through cancellation of previously detected symbolsfrom the received signals and nullification of the non-detected symbols.This process diagonally detects the desired symbol values as many as thenumber of antennas.

The nullification enables the detection of the strongest signal byremoving other weak signals, and the cancellation enables the detectionof the remaining weak signals by removing the previously detectedsignals from the original received signals.

Then, the detected symbols for each antenna are collected by amultiplexer 302, and generated as one data stream in the respectivespace layer, and the data streams of all the antennas are finallycombined in the maximum ratio by a combiner 303.

This maximum ratio combining type is for making the value of an outputsignal-to-interference ratio maximum by applying the respective channelsto gains in proportion to square roots of the signal-to-interferenceratios in the respective channels. These signal-to-interference ratiosin the respective channels are added together to provide a wholesignal-to-interference ratio.

FIG. 4 is a view illustrating another example of a transmitter of aconventional V-BLAST MIMO system. FIG. 5 is a view illustrating anexample of a receiver for receiving signals from the transmitterillustrated in FIG. 4.

According to the MIMO system of FIGS. 4 and 5, the distance betweenantennas is 4λ, and four transmission and reception antennas are used.The MIMO system of FIGS. 4 and 5 is of a vertical-bell labs' layeredspace-time (V-BLAST) type.

The MIMO system of FIGS. 4 and 5 has a similar construction to that ofFIGS. 2 and 3.

However, a signal processor 401 in FIG. 4 simplifies the decodingprocess by simply performing a vector encoding process for changing abit to a symbol. The signal processor 401 modulates and encodes aplurality of sub-data streams divided from one information source. Thatis, M encoded symbols divided from the same information are transmittedthrough a plurality of antennas, respectively.

Also, a detector 501 arranges the M received symbols in the order oftheir levels of the signal-to-interference ratio, and detects a desiredsymbol from the symbols having a good receiving condition among thearranged symbols.

The frequency efficiency of the system used in FIGS. 4 and 5 is lowerthan that of the MIMO system used in FIGS. 2 and 3, but it can beimplemented using a more simplified receiving circuit.

That is, since the transmitted symbols in FIGS. 2 and 3 may suffer afatal error as passing through a multi-paths environment, an obstaclemay arise when the receiver obtains the original information stream fromthe received symbols. Also, the construction of the receiver iscomplicated, and the channel coding is applied in a limited manner.However, the efficiency of the frequency use is heightened.

On the contrary, the system as shown in FIGS. 4 and 5 can be implementedusing a simplified receiving circuit as an alternative, but theefficiency of the frequency use is degraded, and the distance betweenantenna elements should be widened. This is because the distance 10λshould be put between the antennas for no correlation between theantennas, and for practical use, the distance of at least 4λ should beput between the antennas for no correlation (which corresponds to 80% ofthe case having no correlation).

Accordingly, it is required to design a MIMO system that improves theadvantage of the D-BLAST type system illustrated in FIGS. 2 and 3, andmakes up for the weak points in the V-BLAST type system illustrated inFIGS. 4 and 5.

SUMMARY OF THE INVENTION

An object of the present invention is to provide to a method and anapparatus for transmitting/receiving signals in a multiple-inputmultiple-output (MIMO) communication system provided with a plurality ofantenna elements that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

Another object of the present invention is to provide a method and anapparatus for transmitting/receiving signals in a multiple-inputmultiple-output (MIMO) communication system provided with a plurality ofantenna elements having a high efficiency of frequency use.

Another object of the present invention is to provide a method and anapparatus for transmitting/receiving signals in a multiple-inputmultiple-output (MIMO) communication system provided with a plurality ofantenna elements so that enables respective antennas to be efficientlyarranged in a limited space.

Still another object of the present invention is to provide a method andan apparatus for transmitting/receiving signals in a multiple-inputmultiple-output (MIMO) communication system provided with a plurality ofantenna elements that can be easily implemented.

These and other objects and advantages of the present invention areachieved by providing a method and an apparatus fortransmitting/receiving signals in a multiple-input multiple-output(MIMO) communication system provided with a plurality of antennaelements, comprises the steps of dividing the plurality of antennaelements into N groups according to locations of the plurality ofantenna elements, dividing a data stream into N sub-data streamsincluding identifiers of the antenna elements of a corresponding groupand signal-processing the sub-data streams, transmitting an i_(th)processed sub-data stream to a receiver through each antenna element ofan i_(th) group with different transmission delays for i=1, 2, . . . ,and N.

According to another aspect of the present invention, a communicationmethod in a multiple-input multiple-output communication system providedwith a plurality of antenna elements, comprises the steps of dividingthe plurality of transmitting antenna elements into N groups accordingto locations of the plurality of transmitting antenna elements, dividinga data stream into N sub-data streams including identifiers of theantenna elements of a corresponding group, signal-processing thesub-data streams, transmitting an i_(th) processed sub-data stream to areceiver through each transmitting antenna element of an i_(th) groupwith different transmission delays for i=1, 2, . . . , and N, receivingthe processed sub-data streams which are transmitted, detecting antennaelement identifiers of each processed sub-data stream, detecting symbolsfrom the processed i_(th) sub-data stream with different transmissiondelays and its detected antenna element identifiers for i=1, 2, . . . ,and N; and gestoring the data stream by combining the detected symbols.

According to another aspect of the present invention, a method fortransmitting signals in a multiple-input multiple-output communicationsystem provided with a plurality of antenna elements, comprises thesteps of dividing the plurality of antenna elements into N groupsaccording to locations of the plurality of antenna elements, dividing adata stream into N sub-data streams and signal-processing the sub-datastreams, and transmitting an i_(th) processed sub-data stream to areceiver through each antenna element of an i_(th) group with differenttransmission delays for i=1, 2, . . . , N and transmitting identifiersof the antenna elements of the i_(th) group through a seperate channel.

According to another aspect of the present invention, a communicatingmethod in a multiple-input multiple-output communication system providedwith a plurality of antenna elements, comprises the steps of dividingthe plurality of antenna elements into N groups according to locationsof the plurality of antenna elements, dividing a data stream into Nsub-data streams and signal-processing the sub-data streams,transmitting an processed sub-data stream to a receiver through eachantenna element of an i_(th) group with different transmission delaysfor i=1, 2, . . . , N and transmitting identifiers of the antennaelements of the i_(th) group through a separate channel, receiving theprocessed sub-data streams, estimating respective channel vectors of theidentifiers, detecting desired symbols by applying nulling vectors ofthe estimated channel vectors to the processed sub-data streams,respectively, and restoring the data stream by multiplexing the detectedsymbols.

According to another aspect of the present invention, an apparatus fortransmitting signals in a multiple-input multiple-output communicationsystem provided with a plurality of antenna elements, comprises thesteps of N groups into which the apparatus divides the plurality ofantenna elements according to locations of the plurality of antennaelements, a demultiplexer for dividing a data stream into N sub-datastreams including identifiers of the antenna elements of a correspondinggroup, and signal-processor for signal-processing the sub-data streams,wherein the apparatus transmits an i_(th) processed sub-data stream to areceiver through each antenna element of an i_(th) group with differenttransmission delays for i=1, 2, . . . , and N.

According to another aspect of the present invention, a communicationapparatus in a multiple-input multiple-output communication systemprovided with a plurality of antenna elements, comprises N groups intowhich the apparatus divides the plurality of transmitting antennaelements according to locations of the plurality of transmitting antennaelements, a demultiplexer for dividing a data stream into N sub-datastreams including identifiers of the antenna elements of a correspondinggroup and signal-processing the sub-data streams, wherein the apparatustransmits an i_(th) processed sub-data stream to a receiver through eachtransmitting antenna element of an i_(th) group with differenttransmission delays for i=1, 2, . . . , and N, a first detector fordetecting antenna element identifiers of each processed sub-data streamreceived, a second detector for detecting symbols from the processedi_(th) sub-data stream with different transmission delays and itsdetected antenna element identifiers for i=1, 2, . . . , and N, and acombiner for combining the detected symbols to restore the data stream.

According to another aspect of the present invention, an apparatus fortransmitting signals in a multiple-input multiple-output communicationsystem provided with a plurality of antenna elements, comprises N groupsinto which the apparatus divides the plurality of antenna elementsaccording to locations of the plurality of antenna elements, ademultiplexer for dividing a data stream into N sub-data streams, and aprocessor for signal-processing the sub-data streams, wherein theapparatus transmits an i_(th) processed sub-data stream to a receiverthrough each antenna element of an i_(th) group with differenttransmission delays for i=1, 2, . . . , N and transmits identifiers ofthe antenna elements of the i_(th) group through a seperate channel.

According to another aspect of the present invention, a communicatingapparatus in a multiple-input multiple-output communication systemprovided with a plurality of antenna elements, comprises N groups intowhich the apparatus divides the plurality of antenna elements accordingto locations of the plurality of antenna elements, a demultiplexer fordividing a data stream into N sub-data streams, a processor forsignal-processing the sub-data streams; wherein the apparatus transmitsan i_(th) processed sub-data stream to a receiver through each antennaelement of an i_(th) group with different transmission delays for i=1,2, . . . , N and transmits identifiers of the antenna elements of thei_(th) group through a separate channel, a channel estimator forestimating respective channel vectors of the identifiers transmitted, adetector for detecting desired symbols by applying nulling vectors ofthe estimated channel vectors to the processed sub-data streams,respectively, and a multiplexer for multiplexing the detected symbols torestore the data stream.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Additional advantages, objects, and features of the present inventionwill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a diagram illustrating an example of a conventional MIMOsystem;

FIG. 2 is a diagram illustrating an example of a transmitter of aconventional D-BLAST MIMO system;

FIG. 3 is a diagram illustrating an example of a receiver for receivingsignals from the transmitter illustrated in FIG. 2;

FIG. 4 is a diagram illustrating another example of a transmitter of aconventional V-BLAST MIMO system;

FIG. 5 is a diagram illustrating an example of a receiver for receivingsignals from the transmitter illustrated in FIG. 4;

FIG. 6 is a diagram illustrating a transmitter (including four antennaelements) of a MIMO system according to a first embodiment of thepresent invention;

FIG. 7 is a diagram illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 6;

FIG. 8 is a diagram illustrating a second example of a receiver forreceiving signals from the transmitter of FIG. 6;

FIG. 9 is a diagram illustrating a transmitter (including six antennas)of a MIMO system according to a second embodiment of the presentinvention;

FIG. 10 is a diagram illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 9;

FIG. 11 is a diagram illustrating a second example of a receiver forreceiving signals from the transmitter of FIG. 9;

FIG. 12 is a diagram illustrating a third example of a receiver forreceiving signals from the transmitter of FIG. 9;

FIG. 13 is a diagram illustrating a transmitter (including four antennaelements) of a MIMO system according to a third embodiment of thepresent invention;

FIG. 14 is a diagram illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 13;

FIG. 15 is a flowchart illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 13;

FIG. 16A is a diagram illustrating a co-polarized structure of a generalV-BLAST;

FIG. 16B is a diagram illustrating a dual-polarized structure of ageneral V-BLAST; and

FIG. 16C is a diagram illustrating the dual-polarized structure in ahybrid MIMO system according to a fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention suggests a MIMO transmission/reception system thatuses a high efficiency of frequency and a narrow transmission antennadistance. Thus, the present invention provides the advantage of theD-BLAST, and simultaneously supplements the disadvantage of the V-BLASTtype system.

FIG. 6 is a diagram illustrating a transmitter (including four antennaelements) of a MIMO system according to a first embodiment of thepresent invention. FIG. 7 is a diagram illustrating an example of areceiver for receiving signals from the transmitter of FIG. 6.

In FIGS. 6 and 7 is shown a case that the number of transmission antennaelements is the same as that of reception antennas, for example, fourantenna elements are used in total. Also, a D-BLAST transmitter havingat least two antenna elements is considered as a constituent unit, andsuch at least two constituent units constitute a V-BLAST system. Thatis, a plurality of antenna elements are divided into N constituent unitsaccording to locations of the plurality of antenna elements. Herein, adistance between any two antenna elements of each constituent unit isgreater than 1.5 times of a wavelength of the transmitting signal. Adistance between any two antenna elements that belongs to twoconstituent units, respectively, is greater than 4 times of a wavelengthof the transmitting signal. For example, in FIGS. 6 and 7, the distancebetween the antenna elements in the D-BLAST system is 1.5λ in the samemanner as the conventional system. Also, a D-BLAST transmitter isconsidered as a constituent unit of the V-BLAST MIMO system, and theantenna distance of a plurality of D-BLAST transmitters that constitutethe V-BLAST MIMO system is 4λ in the same manner as the conventionalsystem. That is, in case of arranging four antenna elements to implementthe V-BLAST MIMO system, the conventional system requires 12λ, but thesystem according to the present invention requires 7λ only.

Referring to FIG. 6, a pre-encoder 604 adds a header or an indicator fordiscriminating antenna elements of the D-BLAST constituent unit to aninput data stream at its regular intervals. The header or the indicatoris used for discriminating the respective antenna elements of D-BLASTunits of the transmitter when a receiver receives signals through thereceiving antenna elements. For example, the pre-encoder 604 adds aheader or an indicator to each of the M sub-data streams divided fromthe data stream. At this time, the transmitter doesn't use a separatepilot channel when transmitting the data stream, but pilot symbols theheader includes. The receiver receiving the signals generated from thesub-data streams detects the respective headers of the received signalsand knows an antenna element through which a corresponding signal istransmitted.

A demultiplexer 603 divides the data stream into M sub-data streamsincluding the headers or indicators respectively, and provides thedivided sub-data streams to signal processors 602 a and 602 b. Herein, Mcorresponds to a number of the D-BLAST constituent units. At this time,each signal processor 602 a and 602 b is provided with one or at leasttwo sub-data streams including same information. The two signalprocessors 602 a and 602 b arranged in parallel encode and modulate theprovided sub-data streams.

Each binary cyclic shifter 601 a and 601 b shifts the M/2 modulatedsignals in the same D-BLAST constituent unit to the respective antennaelements to transmit the signals to the receiver. For example, theshifter 601 a or 601 b shifts the M/2 modulated signals in the sameD-BLAST constituent unit per 1 symbol interval. Therefore, the M/2modulated signals in the same D-BLAST constituent unit includes sameinformation, different transmission delays, and different pilot symbols.

FIGS. 7 and 8 are diagrams illustrating embodiments of a receiver forreceiving signals from the transmitter of FIG. 6.

Referring to FIG. 7, for example, each of pre-decoders 701 detects theheaders or identifiers of signals received through the antenna elements.For the process, the pre-decoder detects a channel vector of each of thereceived signals. A nulling vector of the channel vector is used to nullundesired symbols (interference and noise signal) of the receivedsignals. A pre-decoder 701 a provides the detected channel vector andthe corresponding received signal to coupled detectors 702 a. At leasttwo adjacent detectors 702 a correspond to a number of the constituentunits. The adjacent detectors 702 a detect desired symbols from thereceived signals for each of the constituent units. The symbols detectedby the adjacent detectors 702 a are provided to a same multiplexer 703a. Accordingly, the symbol sequences provided from the respectivemultiplexers 703 are combined into one symbol sequence in the maximumratio by a combiner 704. For example, if one of the detectors 702 adetects x0, the other does y0, the multiplexer 703 a generates a symbolsequence x0y0. Each of other pre-decoders 702 b-702 c, and 702 d andeach of other coupled multiplexer 703 b, 703 c, and 703 d generate asymbol sequence x1y1 performing the same procedure. Accordingly, symbolssequences x0y0 and x1y1 provided from all multiplexers 703 are combinedinto one symbol sequence xy in the maximum ratio by the combiner 704.

Referring to FIG. 8, for another example, a pre-decoder 801 a recognizesthe headers or identifiers of signals received through the antennaelements. For the process, the pre-decoder 801 a estimates a channelvector of each of the received signals. A nulling vector of the channelvector is used to null undesired symbols (interference and noise signal)of the received signals. The pre-decoder 801 a provides the estimatedchannel vector and the corresponding received signal to coupled detector802 a or 802 b according to a type of the channel vector. Likewise,other pre-decoders 801 b, 801 c, and 801 c do the same according to atype of the channel vector. Accordingly, signals from transmittingantenna elements of a same constituent unit are provided to a samedetector. Each of detectors 802 a and 802 b sequentially detects desiredsymbols using the channel vector and the received signals. For example,one detector 802 a detects x0 and x1 using the channel vectors andreceived signals provided by the pre-decoders 801. The detector 802 acombines the x0 and x1 in the maximum ratio and outputs x. The otherdetector 802 b detects y0 and y1 using them. The detector 802 b combinesthe y0 and y1 in the maximum ratio and outputs y. A multiplexer 803multiplexes the x and y in one symbol sequence xy.

FIG. 9 is a diagram illustrating a transmitter (including six antennaelements) of a MIMO system according to a second embodiment of thepresent invention.

Referring to FIG. 9, the transmission operation of the MIMO systemhaving the odd-numbered D-BLAST constituent units is performed in thesame manner as the system of FIG. 6.

FIGS. 10, 11, and 12 are diagrams illustrating embodiments of a receiverfor receiving signals from the transmitter of FIG. 9.

In FIGS. 9 and 12 is shown a case that the number of transmissionantenna elements is the same as that of reception antenna elements (sixantenna elements in total), and the number of D-BLAST constituent unitsis an odd number. Since the hardware complexity is increased as thenumber of D-BLAST constituent units becomes greater, there is providedone D-BLAST receiver for the D-BLAST constituent units.

Especially, the receiver of FIGS. 10, 11, and 12 is proposed from theviewpoint of reducing the complexity of the receiver by reducing thenumber of D-BLAST detectors even if a more time delay arises where thetransmission antenna elements are increasing. This receiver can beapplied when the MIMO system is used indoors and the mobility is quiteminute. Also, it can be applied when a wireless local loop (WLL) is usedoutdoors.

Referring to FIG. 10, a pre-decoder 1000 estimates respective channelvectors of the received signals. Some portions of the channel vectorsand their received signals are stored in a buffer 1100, others areprovided to a detector 1200. The detector 1200 detects desired symbolsusing the provided channel vectors and their received signals andprovides the detected symbols to the buffer 1100. The detector 1200detects desired symbols using the stored channel vector and theirreceived signals. Such a detection of the symbols and a storage of thedetected symbols are not repeated until the detector 1200 detectsdesired symbols from all the received signal. Symbols having differenttransmission delays and same information among the detected symbols(currently detected symbols and previously detected and stored symbols)are combined into one symbol in the maximum ratio and are provided tothe buffer 1100. A plurality of currently and previously combiningsymbols are simultaneously provided to a multiplexer 1300. Themultiplexer 1300 multiplexes the provided combining symbols as onesymbol sequence. For example, the detector 1200 subsequently detectssymbols x0, x1, y0, and y1 and combines them into respective symbols xand y in the maximum ratio. The detector 1200 provides the x and y tothe buffer 1100. Likewise, the detector 1200 subsequently detectssymbols z0 and z1 and combines them into one symbol z. The x, y, and zare simultaneously provided to the multiplexer 1300. The multiplexer1300 multiplexes the x, y, and z as one symbol sequence. That is, somesignals from antenna elements of one constituent unit among the receivedsignals are stored by the buffer 1100 while others from anotherconstituent unit are used to detect the desired symbols.

Or, referring to FIG. 11, there is provided two first and second buffers1500 and 1600 connected to a D-BLAST detector 1700. Some portions of theestimated channel vector and its received signals are stored by each ofthe buffers 1500 and 1600 according to a type of the channel vectors,others having another type of the channel vector are provided to adetector 1700. At this time, the types of the channel vectors aredetermined based on a same constituent unit in a transmitter. Thedetector 1700 detects desired symbols using the provided channel vectorsand their received signals and provides the detected symbols to one ofthe buffers 1500 and 1600. Thereafter, symbols detected from signalswhich are stored by the first buffer 1500 are stored by the secondbuffer 1600, and they vice versa. The last detected symbols are notstored by a buffer, directly provided to a multiplexer 1800 with thepreviously detected and stored symbols. For example, the detector 1700first detects symbols x0 and x1, which combines into symbol x in themaximum ratio. The x is stored by the first buffer 1500 or second buffer1600. The detector 1700 detects symbols y0 and y1 from signals which arestored by the first buffer 1500, which combines into symbol y in themaximum ratio. The y is stored by the second buffer 1600. The detector1700 detects symbols z0 and z1 from signals which are stored by thesecond buffer 1600, which combines into symbol z in the maximum ratio.The z is directly provided to the multiplexer 1800 with the x and ywithout being stored by a buffer. The multiplexer 1800 multiplexes thex, y, and z as one symbol sequence (xyz).

Or, referring to FIG. 12, each of the pre-decoders 1900 provides theestimated channel vector and its received signals to a detector 2000 aor a buffer 2000 b according to a type of the channel vectors.Accordingly, desired symbols are first detected from signals transmittedthrough antenna elements of one same constituent unit in a transmitter,other symbols are later detected from others, stored by the buffer 2000b, transmitted through antenna elements of another same constituent unittherein. For example, the detector 2000 a detects desired symbols x0,x1, y0, and y1, which combines into respective symbols x and y in themaximum, using the provided channel vectors and their received signals.The detector 2000 a provides the symbols x and y to the buffers 2000 b.Thereafter, the detector 2000 a detects symbols z0 and z1 from signalswhich are stored by the buffer 2000 b, which combines into a symbol z inthe maximum ratio. The z is directly provided to the multiplexer 2100with the x and y without being stored by a buffer. The multiplexer 2100multiplexes the x, y, and z as one symbol sequence (xyz).

The construction of FIGS. 9, 10, 11, and 12 can be used in case that thenumber of transmission antennas is increased to 8, 10, and 12,respectively.

FIG. 13 is a diagram illustrating a transmitter (including four antennaelements) of a MIMO system according to a third embodiment of thepresent invention.

FIG. 14 is a diagram illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 13.

In FIGS. 13 and 14 is shown a case that the number of transmissionantenna elements is the same as that of reception antennas, for example,four antenna elements are used in total. Also, a D-BLAST transmitterhaving at least two antenna elements is considered as a constituentunit, and such at least two constituent units constitute a V-BLASTsystem. That is, a plurality of antenna elements are divided into Nconstituent units according to locations of the plurality of antennaelements. Herein, a distance between any two antenna elements of eachconstituent unit is greater than 1.5 times of a wavelength of thetransmitting signal. A distance between any two antenna elements thatbelongs to two constituent units, respectively, is greater than 4 timesof a wavelength of the transmitting signal. For example, in FIGS. 6 and7, the distance between the antenna elements in the D-BLAST system is1.5K in the same manner as the conventional system. Also, a D-BLASTtransmitter is considered as a constituent unit of the V-BLAST MIMOsystem, and the antenna distance of a plurality of D-BLAST transmittersthat constitute the V-BLAST MIMO system is 4λ in the same manner as theconventional system. That is, in case of arranging four antenna elementsto implement the V-BLAST MIMO system, the conventional system requires12λ, but the system according to the present invention requires 7λ only.

In FIG. 13, a transmitter uses a separate pilot channel for a datastream to be transmitted. The pilot channel are transmitted with a datachannel of the data stream, its transmission chain is not shown.

Referring to FIG. 13, a demultiplexer 2400 divides a data stream into Msub-data streams and provides the divided sub-data streams to signalprocessors 2300 a and 2300 b. At this time, a signal processor 2300 a or2300 b is provided with at least two sub-data streams including sameinformation. The two signal processors 2300 a and 2300 b arranged inparallel encode and modulate the sub-data streams.

A binary cyclic shifter 2200 a or 2200 b periodically connects the M/2modulated signals in the same D-BLAST constituent unit to the respectiveantenna elements to transmit the sub-data streams to the receiver. Forexample, the shifter 2200 a or 2200 b shifts the M/2 modulated signalsto the at least two antenna elements of the same D-BLAST constituentunit per 1 symbol interval. Therefore, the M/2 modulated signals in thesame D-BLAST constituent unit includes same information and differenttransmission delays. The receiver recognizes that a received signal istransmitted through which antenna element. The receiver also estimates achannel condition based on a channel vector of the pilot channel. Italso applies a nulling vector from the channel vector to a receivedsignal resulting in removing an interference and transmission noise thereceived signal includes.

FIG. 14 is a diagram illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 13.

Referring to FIG. 14, a channel estimator 2500 estimates respectivechannel vectors of pilot signals which are transmitted with the receivedsignals. Nulling vectors of the estimated channel vectors are set todetectors 2700 to null undesired symbols respectively. The settingprocess is performed by a nulling vector-setting block 2600. Forexample, where the channel vectors estimated by the channel estimator2500 is designated by “H”, the nulling vector-setting block 2600calculates a pseudo inverse value “H⁺” of “H” using a zero-forcingmethod or an MMSE (Minimum Mean Square Equation) method. And, it sets“H⁺” to one of the detectors 2700. Likewise, another “H” is set toanother of the detectors 2700. Accordingly, one of the detectors 2700applies the set “H⁺” to “SH”, herein “S” designates a received signal.As a result, desired symbols “S” may be obtained. The nullingvector-setting block 2600 provides channel vectors obtained from signalsof a same constituent unit and their nulling vectors to a same detector.That is, the nulling vector-setting block 2600 provides channel vectorsand their nulling vectors to different detectors according to a type ofthe channel vectors. The receiver has the detectors 2700 correspondingto a number of the constituent units of the transmitter. For example,one of the detectors 2700 detects desired symbols x0 and x1, another ofthe detectors 2700 detects desired symbols y0 and y1. The former outputsx, into which x0 and x1 combine in the maximum ratio, the latter outputsy, into which y0 and y1 combine in the maximum ratio. A multiplexer 2800multiplexes the symbols x and y as one symbol (xy).

FIG. 15 is a flowchart illustrating a first example of a receiver forreceiving signals from the transmitter of FIG. 13.

Referring to FIG. 15, the demultiplexer 2400 de-multiplexes a pluralityof sub-data streams including same information for each of sameconstituent units (S10). The signal processors 2300 a and 2300 bchannel-encode and modulate each of the sub-data streams (S11).

Each of the binary cyclic shifters 2200 a and 2200 b shifts themodulated signals at every one symbol delay to transmit the sub-datastreams with different transmission delays for the same D-BLASTconstituent unit to the receiver. A channel estimator 2500 of thereceiver decodes M pilot signals received through receiving antennaelements. That is, the channel estimator 2500 obtains M channel vectors.

The nulling vector-setting vector 2600 sets a nulling vector of theobtained channel vector to one of the detectors 2700 to null undesiredsymbols. As mentioned above, the nulling vector is a pseudo inverse ofthe obtained channel vector according to the zero-forcing method or MMSEmethod. The one detector applies the nulling vector to the receivedsignal and detects desired symbols (x0 x1) or (y0 y1), wherein each ofthe two pair symbols (x0 x1) and (y0 y1) has different transmissiondelays for a same constituent unit. Also, the one detector outputs x,into which x0 and x1 combines in the maximum ratio, another detectoroutputs y, into which y0 and y1 combines in the maximum ratio.

The construction where a polarization diversity is applied in a hybridMIMO system proposed according to the third embodiment of the presentinvention is illustrated in FIGS. 16A to 16C in comparison to theconventional technique.

That is, the third embodiment of the present invention proposes theconstruction where the polarization diversity is applied to the hybridMIMO system supporting an open loop.

Generally, the polarization diversity is classified into a co-polarizedstructure and a dual-polarized structure. The former transmits the samepolarized waves (for example, vertical polarized waves) through therespective antennas, and the latter transmits polarized waves havingdifferent vertical components through the two antennas (for example, avertical polarized wave through the first antenna, and horizontalpolarized wave through the second antenna, and at this time, the firstand second antennas are tilted by 45° and −45°, respectively).

FIG. 16A is a view illustrating a co-polarized structure of a generalV-BLAST.

Herein, in order to reduce the distance between the antennas, the signalis transmitted with 80λ of the transmission capacity when there is nocorrelation, and the distance between the antennas is reduced from 10λto 4λ instead. Accordingly, a space of 6λ in total is required forarranging four transmission antennas, and thus a denser antennastructure can be achieved in comparison to the structure using only thespace diversity.

FIG. 16B is a view illustrating a dual-polarized structure of a generalV-BLAST.

Herein, a space of 6λ in total is required for arranging fourtransmission antennas, and thus a denser antenna structure can beachieved in comparison to the structure using only the space diversity.

FIGS. 6 and 13 are diagrams illustrating the co-polarized structure in ahybrid MIMO system.

Herein, according to the transmission characteristic (each pair ofantennas transmit the same signal, and one of them transmits the signalwith one symbol delay), each pair has the antenna distance of 1.5λ, andthe distance between the pairs is 4λ. Thus a space of 7λ is used for theconstruction of four antennas.

FIG. 16C is a view illustrating the dual-polarized structure in a hybridMIMO system according to a fourth embodiment of the present invention.

In FIG. 16C, the antennas in the same D-BLAST unit are arranged at thesame intervals, and transmit the signals having different transmissiondelay times and different phases (in the present invention, verticalpolarized wave that transmits mutually orthogonal signals). Also, theantennas in the same D-BLAST unit are arranged with a tilt of 45°centering around a reference axis.

At this time, it is sufficient that the whole length where the sameD-BLAST unit is arranged is determined to be ½ of the whole length(i.e., 3.5λ) when the antennas in the same D-BLAST unit transmit thesame phase signal (for example, 7λ).

Accordingly, the antennas may be arranged at the minimum intervals or atlonger intervals for a better transmission ratio. Specifically, eachpair of antennas has the transmitter structure for the simplest D-BLAST,and the whole pairs constitute the V-BLAST transmitter structure.

Also, in addition to the density of the antenna array space, thepolarization diversity provides other advantages in that it provides areception gain in combination with the space diversity if the radiochannel has a high spatial correlation.

Thus, in a weak condition of the MIMO system, it serves to reduce thedeterioration of the transmission capacity.

As described above, the present invention has the following effects.

First, using the composite system of D-BLAST and V-BLAST, the antennadistance is greatly reduced and the frequency efficiency becomes betterin comparison to the widely used V-BLAST system.

Second, using the polarization diversity, a denser system can beconstructed to reduce the base station antenna array distance by 50%.

Third, the deterioration degree of the basic performance of the MIMOsystem that is produced when the channel condition is changed from thenon-correlation condition to the correlation condition due to the changeof the channel continuously changed can be mitigated through thereceiving gain obtained from the effect of the diversity.

Fourth, by reflecting the channel environment continuously changed, thedeterioration degree of the basic performance of the MIMO system that isproduced when the channel condition is changed from the non-correlationcondition to the correlation condition due to the change of the channelcontinuously changed can be mitigated through the construction of aclosed loop and proper power allocation, and at the worst, it can beknown that the performance becomes identical to that of the phased arraysystem.

Fifth, as the correlation of the channels becomes greater, theperformance deterioration can be greater offset in comparison to theopen loop system.

It will be apparent to those skilled in the art than variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for transmitting signals in a multiple-input multiple-outputcommunication system provided with a plurality of antennas, comprising:dividing the plurality of antennas of a transmitter into a plurality ofantenna groups according to locations of the plurality of antennas,wherein each of the antennas included in a same antenna group areseparated apart from each other by at least a first distance and each ofthe antennas included in different antenna groups are separated apartfrom each other by at least a second distance; splitting a data streaminto a plurality of sub-data streams according to a number of theplurality of antenna groups; and transmitting each of the plurality ofsub-data streams with a separately generated sequence of pilot symbolsto a receiver via each antenna included in the corresponding antennagroup from among the plurality of antenna groups, wherein each sequenceof pilot symbols transmitted via each antenna included in thecorresponding antenna group has a predefined pattern that is differentfrom another sequence of pilot symbols transmitted via another antennafrom among the plurality of antennas, and wherein the plurality ofsub-data streams transmitted via each antenna of the plurality ofantenna groups have different phases.
 2. The method of claim 1, whereinthe plurality of sub-data streams transmitted through each antenna ofthe plurality of antenna groups have different transmission delays. 3.The method of claim 1, wherein two or more of the plurality of antennasare included in each of the plurality of antenna groups according to thelocations of the plurality of antennas.
 4. The method of claim 3,wherein each of the sub-data streams is shifted to each antenna includedin each of the plurality of antenna groups before the transmitting. 5.The method of claim 1, wherein the plurality of antenna groups includesa first antenna group and a second antenna group, the first antennagroup having a first antenna and a second antenna, the second antennagroup having a third antenna and a fourth antenna.
 6. The method ofclaim 5, wherein the first antenna of the first antenna group isseparated from the second antenna of the first antenna group by at leastthe first distance, and the third antenna of the second antenna group isseparated from the fourth antenna of the second antenna group by atleast the first distance, wherein the second antenna of the firstantenna group is separated from the third antenna of the second antennagroup by at least the second distance.
 7. The method of claim 6, whereinthe first distance is 1.5 times a wavelength of a transmitting signal.8. The method of claim 6, wherein the second distance is 4 times awavelength of a transmitting signal.
 9. The method of claim 6, whereinthe second distance is greater than the first distance.
 10. The methodof claim 1, wherein the second distance is greater than the firstdistance.
 11. An apparatus for transmitting signals in a multiple-inputmultiple-output communication system, the apparatus comprising: aplurality of antennas divided into a plurality of antenna groupsaccording to locations of the plurality of antennas, wherein each of theantennas included in a same antenna group are separated apart from eachother by at least a first distance and each of the antennas included indifferent antenna groups are separated apart from each other by at leasta second distance; a demultiplexer for splitting a data stream into aplurality of sub-data streams according to a number of the plurality ofantenna groups; and a processor for signal-processing the sub-datastreams with a separately generated sequence of pilot symbols, whereinthe apparatus transmits each of the plurality of sub-data streams with aseparately generated sequence of pilot symbols to a receiver via eachantenna included in the corresponding antenna group from among theplurality of antenna groups, wherein each sequence of pilot symbolstransmitted via each antenna included in the corresponding antenna grouphas a predefined pattern that is different from another sequence ofpilot symbols transmitted via another antenna from among the pluralityof antennas, and wherein the plurality of sub-data streams transmittedvia each antenna of the plurality of antenna groups have differentphases.
 12. The apparatus of claim 11, wherein the plurality of sub-datastreams transmitted through each antenna of the plurality of antennagroups have different transmission delays.
 13. The apparatus of claim11, wherein two or more of the plurality of antennas are included ineach of the plurality of antenna groups according to the locations ofthe plurality of antennas.
 14. The apparatus of claim 13, wherein thesub-data stream is shifted to each antenna included in each of theplurality of antenna groups before each of the sub-data streams istransmitted.
 15. The apparatus of claim 11, wherein the plurality ofantenna groups includes a first antenna group and a second antennagroup, the first antenna group having a first antenna and a secondantenna, the second antenna group having a third antenna and a fourthantenna.
 16. The apparatus of claim 15, wherein the first antenna of thefirst antenna group is separated from the second antenna of the firstantenna group by at least the first distance, and the third antenna ofthe second antenna group is separated from the fourth antenna of thesecond antenna group by at least the first distance, wherein the secondantenna of the first antenna group is separated from the third antennaof the second antenna group by at least the second distance.
 17. Theapparatus of claim 16, wherein the first distance is 1.5 times awavelength of a transmitting signal.
 18. The apparatus of claim 16,wherein the second distance is 4 times a wavelength of a transmittingsignal.
 19. The apparatus of claim 16, wherein the second distance isgreater than the first distance.
 20. The apparatus of claim 11, whereinthe second distance is greater than the first distance.